A normal ear transmits sounds as shown in FIG. 1 through the outer ear 101 to the tympanic membrane (eardrum) 102, which moves the bones of the middle ear 103, which in turn vibrate the oval window and round window openings of the cochlea 104. The cochlea 104 is a long narrow duct wound spirally about its axis for approximately two and a half turns. The cochlea 104 includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The scala tympani forms an upright spiraling cone with a center called the modiolar where the spiral ganglion cells of the acoustic nerve 113 reside. In response to received sounds transmitted by the middle ear 103, the fluid filled cochlea 104 functions as a transducer to generate electric pulses that are transmitted to the cochlear nerve 113, and ultimately to the brain.
Hearing is impaired when there are problems in the ability to transduce external sounds into meaningful action potentials along the neural substrate of the cochlea 104. In some cases, hearing impairment can be addressed by a hearing implant system such as a cochlear implant that electrically stimulates auditory nerve tissue with small currents delivered by multiple electrode contacts distributed along an implant electrode.
FIG. 1 shows some components of a typical cochlear implant system where an external microphone provides an audio signal input to an external signal processing stage 111 which implements one of various known signal processing schemes. The processed signal is converted by the external signal processing stage 111 into a digital data format, such as a sequence of data frames, for transmission into a receiver processor in an implant housing 108. Besides extracting the audio information, the receiver processor in the implant housing 108 may perform additional signal processing, and produces a stimulation pattern (based on the extracted audio information) that is sent through an electrode lead 109 to an implanted electrode array 112 which penetrates into the cochlea 104 through a surgical opening called a cochleostomy. Typically, this electrode array 112 includes multiple electrode contacts 110 on its surface that deliver the stimulation signals to adjacent neural tissue of the cochlea 104 which the brain of the patient interprets as sound. The individual electrode contacts 110 may be activated sequentially or simultaneously in one or more contact groups.
Parents or guardians of non-cooperative hearing implant users (e.g. children) sometimes want to be able to check whether or not the hearing implant system or at least part of it (e.g. the external audio processor) is working properly. That is quite difficult technically. One existing method that allows a subjective evaluation of the front-end audio processing is listening to the sensed audio signal (e.g. from a microphone, telecoil, external audio input, FM system, etc.) by a normal hearing person via a headphone or loudspeaker. This does not allow a detailed diagnosis of the entire hearing implant system, but it is a simple method that allows a normal hearing person to answer the question whether or not a proper audio signal is picked up by the audio processor of the hearing implant system. Defective microphones, telecoils or external audio inputs as well as misadjusted or defective FM systems can be detected, thus making troubleshooting easier.
Existing external processors for hearing implant systems usually provide the internal electric audio signal via mechanical connectors on the outside of the device. These connectors may be directly accessible or may become accessible after the external processor device is disassembled; for example, when the battery pack is detached from the control unit. But the sensed electrical audio signal is not normally available for listening so by a normal hearing person.